The water hyacinth is a floating freshwater plant with beautiful purple flowers and round, glossy green leaves. Originally from South America's Amazon basin, it drifts on the surface of ponds, lakes, and slow-moving rivers, its roots dangling beneath the water instead of anchoring in soil.

While the plant looks lovely, it's become one of the world's most problematic invasive species. Water hyacinths reproduce incredibly fast: a single plant can produce thousands of offspring in just a few months. They spread across waterways like a thick green carpet, sometimes growing so densely that boats can't pass through and fish can't survive underneath because the plants block out sunlight and use up oxygen.

In places where water hyacinth has invaded, entire lakes have been choked with the plants, disrupting fishing, transportation, and water supplies. In Lake Victoria in Africa, huge mats of water hyacinth once covered thousands of acres. People have tried many ways to control it: pulling it out by hand, using special harvesting machines, and even introducing insects that eat the plant.

The water hyacinth shows how a plant that seems harmless in its native habitat can become destructive when introduced somewhere new, without the natural predators and competitors that normally keep its growth in check.